Shayanfar S, Broumand A, Pillai S D
Department of Nutrition and Food Science, National Center for Electron Beam Research, IAEA Collaborating Centre for Electron Beam Technology, Texas A&M University, College Station, TX, USA.
Genomic Signal Processing Lab, Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA.
J Appl Microbiol. 2018 Dec 1;125(6). doi: 10.1111/jam.14081. Epub 2018 Aug 24.
Acid exposure induces accumulation of certain metabolites in bacteria. The experimental objective was to identify the primary metabolites accumulating in Escherichia coli O26:H11 as a function of acid (pH 3·6) exposure.
Different buffers of pH 7·5 and 3·6 were used to study the metabolites accumulating in E. coli O26:H11 cells during such pH exposure. After 24 h of acid exposure, there was a 7-log decline in E. coli populations on trypticase soy agar plates. Untargeted metabolomic analysis identified 293 primary metabolites of which 145 metabolites were differentially (P < 0·01) accumulating between pH 7·5 and 3·6 in E. coli O26:H11.
After 24 h of acid exposure, 21 different metabolic pathways appeared to be functional, suggesting that the cells were still metabolically active. Among the identifiable pathways, the key differentially expressed pathways were associated with peptidoglycan biosynthesis, purine metabolism, d-Glutamine/d-glutamate metabolism, nitrogen metabolism, unsaturated fatty acid biosynthesis and inositol phosphate metabolism.
Shiga toxin producing non-O157 E. coli strains such as E. coli O26 are responsible for a growing number of food-related illnesses in the United States and around the world. From food production to consumption, micro-organisms in foods experience dramatic pH fluctuations by organic acids introduced either during food processing or by inorganic acids in the stomach. Acid exposure induces specific metabolite accumulation in bacterial cells. Understanding the survival mechanisms of pathogenic micro-organisms by studying the metabolome would be helpful in introducing effective hurdles and thus ensuring food safety.
酸暴露会诱导细菌中某些代谢物的积累。本实验的目的是确定在大肠杆菌O26:H11中随着酸（pH 3·6）暴露而积累的主要代谢物。
使用pH 7·5和3·6的不同缓冲液来研究在这种pH暴露期间大肠杆菌O26:H11细胞中积累的代谢物。酸暴露24小时后，胰蛋白酶大豆琼脂平板上的大肠杆菌数量下降了7个对数级。非靶向代谢组学分析鉴定出293种主要代谢物，其中145种代谢物在大肠杆菌O26:H11的pH 7·5和3·6之间差异积累（P < 0·01）。
酸暴露24小时后，21条不同的代谢途径似乎仍在发挥作用，这表明细胞仍具有代谢活性。在可识别的途径中，关键的差异表达途径与肽聚糖生物合成、嘌呤代谢、d-谷氨酰胺/d-谷氨酸代谢、氮代谢、不饱和脂肪酸生物合成和肌醇磷酸代谢有关。
产志贺毒素的非O157大肠杆菌菌株，如大肠杆菌O26，在美国和世界各地导致越来越多与食物相关的疾病。从食品生产到消费，食品中的微生物会因食品加工过程中引入的有机酸或胃中的无机酸而经历剧烈的pH波动。酸暴露会诱导细菌细胞中特定代谢物的积累。通过研究代谢组来了解致病微生物的生存机制，将有助于引入有效的障碍，从而确保食品安全。
